Frequently Asked Questions about Magneto-Electric Rotation Detector

MP-981 Operating Principle

The MP-981 Magneto-Electric Rotation Detector incorporates a magnetoresistive element, permanent magnet, DC amplifier, and voltage regulator to measure gear rotation speeds from very low to high speeds (1 to 20 kHz).

The MP-981 has a detection section equipped with a magnetoresistive element at the tip of the sensor. This detection section consists of two magnetoresistive elements, MR1 and MR2, and a magnet. By shaping the signal waveform detected by this detection section, the MP-981 obtains a square wave output.

Circuit block diagram

The detection unit consists of two magnetoresistive elements MR1 and MR2 and a magnet, as shown in the figure below. Magnetoresistive elements exhibit resistance values proportional to the magnitude of the applied magnetic field. When a magnetic material (gear) is present in front of the sensor, the strength of the magnetic field changes. Therefore, if the position of the magnetic material is unbalanced with respect to each magnetoresistive element, the resistance values will also be unbalanced. As shown in the figure below, when a constant voltage is applied between terminals 1-3 and the output voltage of terminal 2 is observed, the output signal from terminal 2 changes in a way that traces the shape of the gear.

The signal obtained from the magnetoresistive sensor is waveform-shaped to produce the final signal. Because the amplitude of the signal obtained from the magnetoresistive sensor is small (tens of mV), changes in the midpoint voltage due to temperature changes or increases in rotational speed can cause changes in the duty cycle or loss of pulse output.